import sys, os, time, atexit
from signal import SIGTERM 

class Daemon:
        """
        A generic daemon class.
        
        Usage: subclass the Daemon class and override the run() method
        """
        def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
                self.stdin = stdin
                self.stdout = stdout
                self.stderr = stderr
                self.pidfile = pidfile
        
        def daemonize(self):
                """
                do the UNIX double-fork magic, see Stevens' "Advanced 
                Programming in the UNIX Environment" for details (ISBN 0201563177)
                http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
                """
                try: 
                        pid = os.fork() 
                        if pid > 0:
                                # exit first parent
                                sys.exit(0) 
                except OSError, e: 
                        sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
                        sys.exit(1)
        
                # decouple from parent environment
                #os.chdir("/") 
                os.setsid() 
                os.umask(0) 
        
                # do second fork
                try: 
                        pid = os.fork() 
                        if pid > 0:
                                # exit from second parent
                                sys.exit(0) 
                except OSError, e: 
                        sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
                        sys.exit(1) 
        
                # redirect standard file descriptors
                sys.stdout.flush()
                sys.stderr.flush()
                si = file(self.stdin, 'r')
                so = file(self.stdout, 'a+')
                se = file(self.stderr, 'a+', 0)
                os.dup2(si.fileno(), sys.stdin.fileno())
                os.dup2(so.fileno(), sys.stdout.fileno())
                os.dup2(se.fileno(), sys.stderr.fileno())
        
                # write pidfile
                #atexit.register(self.delpid)
                pid = str(os.getpid())
                file(self.pidfile,'w+').write("%s\n" % pid)
        
        def delpid(self):
                os.remove(self.pidfile)

        def start(self):
                """
                Start the daemon
                """
                # Check for a pidfile to see if the daemon already runs
                try:
                        pf = file(self.pidfile,'r')
                        pid = int(pf.read().strip())
                        if pid:
                                if not os.path.exists('/proc/'+ str(pid)):
                                        self.delpid()
                                        pid = None
                        pf.close()
                except IOError:
                        pid = None
        
                if pid:
                        message = "pidfile %s already exist. Daemon already running\n"
                        sys.stderr.write(message % self.pidfile)
                        sys.exit(1)
                
                # Start the daemon
                self.daemonize()
                self.run()

        
        def status(self):
                """
                Status of de daemon
                """
                # Get the pid from the pidfile
                try:
                        pf = file(self.pidfile,'r')
                        pid = int(pf.read().strip())
                        pf.close()
                except IOError:
                        pid = None
        
                if not pid:
                        message = "Daemon not running\n"
                        sys.stdout.write(message)
                        return # not an error in a restart
                else:
                        if not os.path.exists('/proc/'+ str(pid)):
                                message = "Daemon not running\n"
                                sys.stdout.write(message)
                                self.delpid()
                                pid = None
                                return
                        else:
                                message = "Daemon is running\n"
                                sys.stdout.write(message)


        def stop(self):
                """
                Stop the daemon
                """
                # Get the pid from the pidfile
                try:
                        pf = file(self.pidfile,'r')
                        pid = int(pf.read().strip())
                        pf.close()
                except IOError:
                        pid = None
        
                if not pid:
                        message = "pidfile %s does not exist. Daemon not running?\n"
                        sys.stderr.write(message % self.pidfile)
                        return # not an error in a restart

                # Try killing the daemon process        
                try:
                        while 1:
                                os.kill(pid, SIGTERM)
                                time.sleep(0.1)
                except OSError, err:
                        err = str(err)
                        if err.find("No such process") > 0:
                                if os.path.exists(self.pidfile):
                                        os.remove(self.pidfile)
                        else:
                                print str(err)
                                sys.exit(1)

        def restart(self):
                """
                Restart the daemon
                """
                self.stop()
                self.start()

        def run(self):
                """
                You should override this method when you subclass Daemon. It will be called after the process has been
                daemonized by start() or restart().
                """
